Locking mechanism for a bone screw

ABSTRACT

A locking mechanism for securing a bone screw  20  to a clamping element  30  of an osteosynthesis holding system  5  is provided. The bone screw  20  has a circumferential groove  25  located on a top portion of the screw  20  below a screw head  22.  Snap catches  35  protrude from a bone-contacting surface  38  of the clamping element  30  and interlock with the groove  25  in the screw  20  when the screw  20  is inserted into the clamping element  30  (e.g., when the screw is screwed into a bone segment through a hole in the clamping element). A removal device  90  is provided for removing the screw  20,  as a greater axial force is required to overcome the locking mechanism than is needed to engage the locking mechanism. A method for revision (removal) of the screw  20  from the locking mechanism is also provided.

This application claims the benefit of U.S. provisional patentapplication No. 60/262,968 filed on Jan. 19, 2001.

BACKGROUND OF THE INVENTION

The present invention relates generally to osteosynthesis holdingsystems, such as those used for stabilization of the spinal column. Inparticular, a locking mechanism for securing a bone screw to a clampingelement of an osteosynthesis holding system is provided. A removaldevice is provided for removing the bone screw, as a greater axial forceis required to overcome the locking mechanism than is needed to engagethe locking mechanism. A corresponding method for revision (removal) ofthe bone screw from the locking mechanism is also provided.

It is well known that in osteosynthesis holding systems in general, andin those systems used for stabilization of the spinal column inparticular, a loosening of the bone screw which secures the clampingelement to the bone segment occurs. When the bone screw becomes loose,the bone screw may move in an axial direction (i.e. a backing out of thescrew may occur). This axial movement may result in a loosening of theentire system, as well as injury to the patient by the protruding screw.For example, injury of blood vessels and nerves in the cervical spineand esophagus are common.

Several alternatives exist for securing the bone screw to the bone plateor clamping element. For example, attachment or locking screws orexpansion elements may be used to secure the bone screw in place.

It would be advantageous to provide a locking mechanism for a bone screwwhere no additional securing elements are necessary. It would be furtheradvantageous to provide a locking mechanism where no active locking ofthe bone screw is needed. It would be still further advantageous if theconnection formed by the locking mechanism is reversible, to provide forexplantation (removal) of the bone screw. In addition, it would beadvantageous if the locking mechanism allows for a pre-stressing of thebone screw between the clamping element and the bone segment after thelocking element is engaged.

The methods and apparatus of the present invention provide the foregoingand other advantages.

SUMMARY OF THE INVENTION

The present invention relates to a locking mechanism for securing a bonescrew to a clamping element of an osteosynthesis holding system. Thebone screw is provided with a circumferential groove located on a topportion of the screw below a screw head. Snap catches are provided onthe clamping element. The snap catches protrude from a bone-contactingsurface of the clamping element and interlock with the groove in thebone screw when the bone screw is inserted into the clamping element(e.g., when the screw is screwed into a bone segment through a hole inthe clamping element). A removal device is provided for removing thebone screw, as a greater axial force is required to overcome the lockingmechanism than is needed to engage the locking mechanism. Acorresponding method for revision (removal) of the bone screw from thelocking mechanism is also provided.

In an exemplary embodiment, a locking mechanism for a bone screw isprovided. The locking mechanism includes a clamping element forstabilizing bone segments. The clamping element has at least two snapcatches which protrude from a bone-contacting surface of the clampingelement and are spaced around an edge of a screw hole. A bone screw isprovided which has a circumferential groove located on a top portionthereof below a screw head, for receipt of said snap catches. The snapcatches interlock with the groove to secure said bone screw to theclamping element when the bone screw is inserted into the clampingelement.

The snap catches may comprise spikes adapted to act as bone anchors.These spikes provide additional anchoring of the clamping element intothe bone segment. The spikes may comprise elastic spring elements whichsnap into the groove when the bone screw is inserted into the clampingelement.

In a preferred embodiment, the bone screw is removable from the clampingelement after the snap catches interlock with the groove. However, it ispreferable if a greater axial force is needed to remove the screw fromthe clamping element than is needed to insert the screw into theclamping element. Removal of the screw from the clamping element mayresult in deformation of the snap catches and/or the groove.

The screw may have a shaft having a conical portion between the grooveand threads of the shaft. The groove may have a flat edge portionperpendicular to the shaft of the screw. The snap catches may have asquare end portion for interlocking with the flat edge portion. Removalof the screw from the clamping element may result in deformation of atleast one of (i) the square end portion of the snap catches, or (ii) theflat edge portion of the groove.

A targeting instrument may be placed on the clamping element to providefor correct axial positioning of the screw. The screw is screwed throughthe clamping element and into the bone segment via the targetinginstrument.

The screw may be a cannulated screw. The cannulated screw may bepositioned on the bone segment via a Kirschner wire.

The screw may be rotatable after interlocking with the clamping elementin order to achieve further pre-stress between the bone segment and theclamping element.

The screw may be a cannulated screw having internal threads in acannulated portion thereof. The screw may be removable from the clampingelement using a removal device having (i) an externally threaded distalend for engagement with the internal threads of the cannulated portionof the screw, and (ii) a handle at a proximal end. The removal device isadapted to be inserted into the screw via a cannulated screwdriver.Removal of the screw is possible by unscrewing the screw from the bonesegment using the cannulated screwdriver while simultaneously pulling onthe removal device.

The invention further provides for a removal device for revision(removal) of an internally threaded cannulated bone screw. The removaldevice has a wire body with external threads at a distal end thereof forengagement with the internal threads of the screw. A handle is providedat a proximal end of the wire body for use in pulling the removal deviceafter engagement with the cannulated screw.

The removal device is adapted for insertion into a cannulatedinstrument, such as a cannulated screwdriver.

The invention also provides a method for revision of an implantedcannulated bone screw. A cannulated screwdriver is inserted into a screwhead of the cannulated bone screw. A removal device is inserted into thecannulated screwdriver. An externally threaded distal end of the removaldevice is screwed into an internally threaded portion of the cannulatedscrew. Once the removal device is screwed into the cannulated bonescrew, the screw can be removed (e.g., from a bone segment) bysimultaneously unscrewing the screw using the cannulated screwdriver andpulling the screw using a handle located on a proximal end of theremoval device.

The bone screw to be removed may secure a clamping element to a bonesegment. A locking mechanism may secure the bone screw to the clampingelement. The locking mechanism comprises at least two snap catchesprotruding from a bone-contacting surface of the clamping element andspaced around an edge of a screw hole. A circumferential groove islocated on a top portion of the screw below a screw head for receipt ofthe snap catches. The snap catches interlock with the groove to securethe bone screw to the clamping element when the bone screw is screwedinto the bone segment through the screw hole of the clamping element.

The snap catches may comprise spikes adapted to function as boneanchors. The spikes may comprise elastic spring elements which snap intothe groove when the bone screw is inserted into the clamping element. Agreater axial force may be needed to remove the screw from the clampingelement than is needed to insert the screw into the clamping element.Removal of the screw from the clamping element results in deformation ofat least one of (i) the snap catches, or (ii) the groove.

The screw comprises a shaft having a conical portion between the grooveand threads of the shaft. The groove may have a flat edge portionperpendicular to a shaft of the screw. The snap catches may have asquare end portion for interlocking with the flat edge portion. Removalof the screw from the clamping element results in deformation of atleast one of (i) the square end portion of the snap catches, or (ii) theflat edge portion of the groove.

The screw may be rotatable after interlocking with the clamping elementin order to achieve further pre-stress between the bone segment and theclamping element.

A method for locking a bone screw to a clamping element is alsoprovided. A clamping element for stabilizing bone segments is provided.The clamping element has at least two snap catches protruding from abone-contacting surface of the clamping element and spaced around anedge of a screw hole. A bone screw is provided which has acircumferential groove located on a top portion thereof below a screwhead, for receipt of said snap catches. The bone screw is screwed intothe bone segment through the screw hole of the clamping element untilthe snap catches interlock with the groove to secure the bone screw tothe clamping element.

The snap catches may comprise spikes adapted to function as boneanchors. The spikes may comprise elastic spring elements which snap intothe groove when the bone screw is inserted into the clamping element.

The bone screw may be removable from the clamping element after the snapcatches interlock with the groove. A greater axial force may be neededto remove the screw from the clamping element than is needed to insertthe screw into the clamping element. Removal of the screw from theclamping element may result in deformation of at least one of (i) thesnap catches, or (ii) the groove.

The screw may comprise a shaft having a conical portion between thegroove and threads of the shaft. The groove may have a flat edge portionperpendicular to a shaft of the screw. The snap catches may have asquare end portion for interlocking with the flat edge portion. Removalof the screw from the clamping element may result in deformation of atleast one of (i) the square end portion of the snap catches, or (ii) theflat edge portion of the groove.

A targeting instrument may be placed on the clamping element to providefor correct axial positioning of the screw. The screw may be screwedthrough the clamping element and into the bone segment via the targetinginstrument.

The screw may be a cannulated screw. The cannulated screw may bepositioned on the bone segment via a Kirschner wire.

The screw may be rotatable after interlocking with the clamping elementin order to achieve further pre-stress between the bone segment and theclamping element.

The screw may be a cannulated screw having internal threads in acannulated portion thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will hereinafter be described in conjunction withthe appended drawing figures, wherein like numerals denote likeelements, and:

FIG. 1 shows an example of an osteosynthesis holding system with oneembodiment of the locking mechanism of the present invention;

FIG. 2 shows a side view of the osteosynthesis holding system of FIG. 1;

FIG. 3 shows a top view of the osteosynthesis holding system of FIG. 2;

FIG. 4 shows an example embodiment of the locking mechanism of thepresent invention;

FIG. 5 shows an example embodiment of the locking mechanism of thepresent invention;

FIG. 6 shows a close up view of an example embodiment of the presentinvention;

FIG. 7 shows a targeting instrument for use in inserting a bone screwinto an osteosynthesis plating system which utilizes an embodiment ofthe locking mechanism of the present invention;

FIG. 8 shows a removal device for use in removing a screw from anosteosynthesis plating system having a locking mechanism in accordancewith the present invention; and

FIG. 9 shows a removal device used with a cannulated screwdriver toremove a screw from an osteosynthesis plating system having a lockingmechanism in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The ensuing detailed description provides preferred exemplaryembodiments only, and is not intended to limit the scope, applicability,or configuration of the invention. Rather, the detailed description ofthe preferred exemplary embodiments will provide those skilled in theart with an enabling description for implementing a preferred embodimentof the invention. It should be understood that various changes may bemade in the function and arrangement of elements without departing fromthe spirit and scope of the invention as set forth in the appendedclaims.

The present invention relates to a locking mechanism for securing a bonescrew to a clamping element of an osteosynthesis holding system. Anexample embodiment of an osteosynthesis holding system with which thepresent invention can be implemented is described in detail in commonlyassigned U.S. Pat. No. 6,206,879 entitled “Osteosynthetic HoldingSystem.” Although the present invention will be described in connectionwith a twin screw osteosynthesis holding system of the type described inU.S. Pat. No. 6,206,879, those skilled in the art will appreciate thatthe locking mechanism of the present invention can be utilized in asingle screw osteosynthesis holding systems, as well as a wide varietyof applications where a screw needs to be secured to a clamping elementor similar device.

FIG. 1 shows an end view of an exemplary embodiment of an osteosynthesisholding system 5 with the locking mechanism of the present invention. Abrief description of the osteosynthesis holding system will enablebetter understanding of the inventive locking mechanism. Theosteosynthesis holding system 5 is a twin screw holding system, having astabilizing screw 10 and an anchoring screw 20. A clamping element 30 isprovided which secures a connector 40 (which can comprise, e.g., a plateor rods or the like) in position on a bone segment (not shown) bytightening a fixation nut 50, which screws onto stabilizing screw 10.The connector 40 is clamped at each end by respective clamping elements30 which are anchored to respective bone segments for stabilizing thebone segments relative to one another.

A side view of the osteosynthesis holding system 5 of FIG. 1 is shown inFIG. 2. FIG. 2 shows the osteosynthesis holding system assembled toconnect two bone segments (not shown). Therefore, a clamping element 30is provided for each bone segment, and a corresponding anchor screw 20is also provided for each segment. The connector 40 spans the twoclamping elements and is secured to each by a respective fixation nut50. Respective stabilizing screws 10 (not visible in side view of FIG.2) are also provided for each clamping element 30.

FIG. 3 shows a top view of the osteosynthesis holding system 5 of FIGS.1 and 2. The top view of FIG. 3 shows the connector 40 spanning the twoclamping elements 30, and secured thereto by respective fixation nuts 50on respective stabilizing screws 10. Respective anchoring screws 20 arealso provided for each clamping element 30.

In the example embodiment of the invention shown in FIGS. 1-3, a lockingmechanism for a bone screw (e.g., anchoring screw 20) is provided. Thelocking mechanism includes a clamping element 30 for stabilizing bonesegments. The clamping element 30 has at least two snap catches 35 whichprotrude from a bone-contacting surface 38 of the clamping element 30and are spaced around an edge of a screw hole 31 (shown in dot-dashedlines) in the clamping element 30. A bone screw 20 is provided which hasa circumferential groove 25 located on a top portion thereof below ascrew head 22, for receipt of said snap catches. The snap catches 35interlock with the groove 25 to secure the bone screw 20 to the clampingelement 30 when the bone screw 20 is inserted into the clamping element30.

No positive locking is required with the locking mechanism of thepresent invention, as the snap catches 35 automatically lock into thegroove 25 when the bone screw 20 is inserted into the clamping element30 and tightened so as to secure the clamping element 30 to the bonesegment.

FIG. 4 shows an example embodiment of the locking mechanism of thepresent invention. Snap catches 35 protrude from a bone contactingsurface of the clamping element 30 (only partially shown in FIG. 4). Thesnap catches 35 may comprise spikes 36 adapted to act as bone anchors.These spikes 36 provide additional anchoring of the clamping element 30into the bone segment.

The spikes 36 may comprise elastic spring elements which snap into thegroove 25 when the bone screw 20 is inserted into the clamping element30. For example, the spikes 36 may have a resilient structure thatenables the snap catches 35 to be expanded by the insertion of the screw20 into the clamping element 30. When the screw 20 is sufficientlyinserted into the clamping element 30 such that the groove 25 alignswith the snap catches 35, the snap catches resiliently return to theirnatural position, thereby interlocking with the groove 25.

As shown in FIG. 4, the screw 20 may be a cannulated screw havinginternal threads 27 in a cannulated portion thereof.

In a preferred embodiment, the bone screw 20 is removable from theclamping element 30 after the snap catches 35 interlock with the groove25. However, it is preferable if a greater axial force is needed toremove the screw 20 from the clamping element 30 than is needed toinsert the screw 20 into the clamping element 30. Removal of the screw20 from the clamping element 30 may result in deformation of the snapcatches 35 and/or the groove 25.

As shown in FIG. 5, the screw 20 may have a shaft 21 having a conicalportion 23 between the groove 25 and threads 28 of the shaft 21. Asshown in FIG. 6, the groove 25 may have a flat edge portion 26perpendicular to the shaft 21 of the screw 20. The snap catches 35 mayhave a square end portion 39 for interlocking with the flat edge portion26 of the groove 25. Removal of the screw 20 from the clamping element30 may result in deformation of at least one of (i) the square endportion 39 of the snap catches 35, or (ii) the flat edge portion 26 ofthe groove 25.

As shown in FIG. 7, a targeting instrument 80 may be placed on theclamping element 30 to provide for correct axial positioning of thescrew 20. The screw 20 is inserted through the targeting instrument 80in the direction indicated by arrow A and into a screw hole of theclamping element 30. The screw 20 is then screwed through the clampingelement 30 and into the bone segment (not shown) via the targetinginstrument.

The screw 20 may be a cannulated screw. The cannulated screw may bepositioned on the bone segment via a Kirschner wire as well known in theart.

The screw 20 may be rotatable after interlocking with the clampingelement 30 in order to achieve further pre-stress between the bonesegment and the clamping element 30.

As shown in FIG. 8, the invention further provides for a removal device90 for revision (removal) of an internally threaded cannulated bonescrew 20. The removal device 90 has a wire body 91 with external threads92 at a distal end thereof for engagement with the internal threads 27of screw 20. A handle 94 is provided at a proximal end of the wire body91 for use in pulling the removal device 90 after engagement with thecannulated screw 20.

As shown in FIG. 9, the removal device 90 is adapted to be inserted intothe screw 20 via a cannulated screwdriver 110. Removal of the screw isaccomplished by inserting the cannulated screwdriver 110 into a screwhead 22 of the cannulated bone screw 20. The cannulated screwdriver hasa drive head 120 for engagement with a corresponding recess on the screwhead 22. The drive head 120 and corresponding recess in the screw head22 may be, for example, hexagonal in shape. The removal device 90 isinserted into the cannulated screwdriver 110. As can be seen in FIGS. 4and 5, an externally threaded distal end 92 of the removal device 90 isscrewed into internal threads 27 of the cannulated screw 20. Once theremoval device 90 is screwed into the cannulated bone screw 20, thescrew 20 can be removed (e.g., from a bone segment 100) bysimultaneously unscrewing (Arrow B) the screw using the cannulatedscrewdriver 110 and pulling (Arrow C) the screw 20 using the handle 94located on a proximal end of the removal device 90.

Due to the configuration of the locking mechanism of the presentinvention, a greater axial force may be needed to remove the screw 20from the clamping element 30 than is needed to insert the screw 20 intothe clamping element 30. The removal device 90 provides assistance ingenerating the axial force required to overcome the locking mechanism.As discussed above, removal of the screw 20 from the clamping element 30may result in deformation of at least one of (i) the snap catches 35, or(ii) the groove 25.

Corresponding methods for locking the 20 bone screw to the clampingelement 30 are also provided. The bone screw 20 is screwed into a bonesegment through the screw hole of the clamping element 30 until the snapcatches 35 interlock with the groove 25 to secure the bone screw 20 tothe clamping element 30. A targeting instrument 80 (FIG. 7) may beplaced on the clamping element 30 to provide for correct axialpositioning of the screw 20. The screw 20 may be screwed through theclamping element 30 and into the bone segment via the targetinginstrument 80.

As noted above, the screw 20 may be a cannulated screw. Moreover, thecannulated screw may be positioned on the bone segment via a Kirschnerwire.

It should now be appreciated that the present invention providesadvantageous methods and apparatus for locking a bone screw to aclamping element, as well as advantageous methods and apparatus forremoving a bone screw with such a locking mechanism from a clampingelement.

Although the invention has been described in connection with variousillustrated embodiments, numerous modifications and adaptations may bemade thereto without departing from the spirit and scope of theinvention as set forth in the claims.

What is claimed is:
 1. A locking mechanism for a bone screw, comprising:a clamping element for stabilizing bone segments, having at least twosnap catches protruding from a bone-contacting surface of said clampingelement and spaced around an edge of a screw hole of the clampingelement; and a bone screw having a circumferential groove located on atop portion thereof below a screw head, for receipt of said snapcatches; wherein said snap catches interlock with said groove to securesaid bone screw to said clamping element when said bone screw isinserted into said clamping element.
 2. A locking mechanism inaccordance with claim 1, wherein: said snap catches comprise spikesadapted to act as bone anchors.
 3. A locking mechanism in accordancewith claim 2, wherein: said spikes comprise elastic spring elements; andsaid elastic spring elements snap into said groove when said bone screwis inserted into said clamping element.
 4. A locking mechanism inaccordance with claim 1, wherein said bone screw is removable from saidclamping element after said snap catches interlock with said groove. 5.A locking mechanism in accordance with claim 4, wherein a greater axialforce is needed to remove said screw from said clamping element than isneeded to insert said screw into said clamping element.
 6. A lockingmechanism in accordance with claim 4, wherein: removal of said screwfrom said clamping element results in deformation of at least one of (i)said snap catches, or (ii) said groove.
 7. A locking mechanism inaccordance with claim 1, wherein: said screw comprises a shaft having aconical portion between said groove and threads of said shaft.
 8. Alocking mechanism in accordance with claim 1, wherein: said groove has aflat edge portion perpendicular to a shaft of said screw; and said snapcatches have a square end portion for interlocking with said flat edgeportion.
 9. A locking mechanism in accordance with claim 8, wherein:removal of said screw from said clamping element results in deformationof at least one of (i) said square end portion of said snap catches, or(ii) said flat edge portion of said groove.
 10. A locking mechanism inaccordance with claim 1, wherein: a targeting instrument is placed onsaid clamping element; and said screw is screwed through said clampingelement and into said bone segment via said targeting instrument.
 11. Alocking mechanism in accordance with claim 1, wherein: said screw is acannulated screw; and said screw is positioned on the bone segment via aKirschner wire.
 12. A locking mechanism in accordance with claim 1,wherein: said screw is rotatable after interlocking with said clampingelement in order to achieve further pre-stress between said bone segmentand said clamping element.
 13. A locking mechanism in accordance withclaim 1, wherein: said screw is a cannulated screw having internalthreads in a cannulated portion thereof.
 14. A locking mechanism inaccordance with claim 13, wherein: said screw is removable from saidclamping element using a removal device having (i) an externallythreaded distal end for engagement with said internal threads of saidcannulated portion of said screw, and (ii) a handle at a proximal end;said removal device is adapted to be inserted into said screw via acannulated screwdriver; and removal of said screw is possible byunscrewing said screw from said bone segment using said cannulatedscrewdriver while simultaneously pulling on said removal device.